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Using enthalpies of formation

Using enthalpies of formation - Using enthalpies of...

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Using enthalpies of formation ( f ) to calculate enthalpies of reaction under standard conditions (∆ rxn ) We can determine the standard enthalpy change for any reaction ( rxn ) by using standard enthalpies of formation ( f ) and Hess's Law Consider the following combustion reaction of propane: C 3 H 8 ( g ) + 5O 2 ( g ) -> 3CO 2 ( g ) + 4H 2 O( l ) The reactants : The standard heat of formation ( f ) of propane gas from its elemental constituents in the standard state is 103.85 kJ/mole 3C( graphite ) + 4H 2 ( g ) -> C 3 H 8 ( g ) f = -103.85 kJ The standard heat of formation ( f ) for O 2 ( g ) is zero O 2 ( g ) -> O 2 ( g ) €∆ f = 0 kJ and so. .. 5O 2 ( g ) -> 5O 2 ( g ) €∆ f = 0 kJ Overall, therefore, the standard heat of formation ( f ) for the reactants is: 3C( graphite )+4H 2 ( g )+5O 2 ( g ) -> C 3 H 8 ( g )+5O 2 ( g ) f = -103.85 kJ The products: The standard heat of formation (
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